Frequency divider



Jilly 31, 1951 J. B. ATWOOD FREQUENCY DIVIDER Filed Dec. 12, 1947INVENTOR JOHN B. ATWOOD .S'UPPL Y AT RNEY Patented July 31 1951FREQUENCY invites 4 g John B. Atwood, Biverhead, N. Y.-, as'signor toRadio Corporation of America, a corporation of Delaware ApplicationDecember 12, 1947', serial 7.91.400

5 Claims.

'tube'with a change in the cathode heater voltage supply during thedischarge time of the storage condenser.

An object of the present invention is to provide a frequency divider orcounter having improved stability despite changes in voltage of thecathode heater supply.

Another object is to provide a frequency divider or counter capable ofcounting pulses over an extremely wide band of frequencies at a constantfixed integer and with relatively good stability with changes of cathodeheater voltage.

A further object is to provide a frequency divider capable of countingpulses over anextremely wide band of frequencies (repetition rates) ofthe pulses to be divided.

A feature of the invention is the use of an extra vacuum tube fordischarging the storage condenser, and a resistor for assuring. that themajor .portion of the discharge passes through this extra vacuum tube.

Av detailed description of the invention follows in conjunction with adrawing, wherein:

Figs. 1 and 2 illustrate two different frequency dividers embodying theprinciples of the invention. In the drawing, the same or equivalentparts are designated by the same reference characters.

Referring to Fig. 1, the frequency divider includesa pair of diodes DIand D2 which, if desired, may be in a single envelope,sand which arefedby the pulses to be counted or divided from lead Hi and throughcondenser II. The cathode of DI is directly connected to the anode of D2and both of these electrodes are connected to condenser II. The anode ofdiode DI is grounded, while the cathode of D2 is connected to storagecondenser 0 across which a step wave voltage is developed. Each step orstair of this developed step wave voltage corresponds to an increment ofvoltage built-up in response to a pulse applied to input lead Ill.Condenser .II :is. appreciably. smaller in 1 size than condenvacuum tubeVI.

nected to a point between winding 2 of transser 0 and these condensersmay have a relation, for example, of 1:5 depending upon the number ofpulses to be counted; or stated otherwise, depending upon the constantfixed integer or factor by which the frequency of the input pulses'is tobe divided:

The cathode of diode D2 is also connected to one terminal of winding 2of a three-winding pulse transformer T. -The other terminal of winding 2is connected through a resistor R to the control grid of a vacuum tubeV2. The anode of tube V2 is connected through winding I of transformerTto the plus or positive terminal of a source of unidirectionalpotential I2 whose negative terminal is connected to ground.- A bleedernetwork Isis connected across the source I2, and a tap it on thisbleeder is connected to the cathode of tube V2 for supplying a positivepotential to this cathode of sufficient magnitude to normally bias tubeV2 beyond cut-off. The bias for tube V2 can be varied by varying tap I4.

The third winding e of transformer T is shunted by a damping resistor I5and is connected between ground and the control grid of discharge Theanode of tube VI is conformer T and resistor R. The cathode of tube VIis connected by way of lead Is to a, point on bleeder 13'. so as to biasthis tubeVI beyond cut-off. The cathodes of tubes VI and V2 are alsoconnected to ground through bypass condensers I6 and H, respectively.

In. the operation of the frequency divider of Fig. 1, the bias on tubeV2 is set by means of tap I 3 so that anode current through tube V2 willbe cut-01f until the voltage supplied to its grid from storage condenserC reaches a predetermined magnitude sufiicient to overcome this cut-offbias. The'values of condensers II and C and the setting of tap it are socorrelated that the frequency divider counts the desired number of inputpulses before tube V2 conducts and causes storage condenser C todischarge.

Let it be assumed that the frequency divider is to divideby 5, and'thatthe input impulses applied to lead I0 are positive in polarity, On

creaseinchargeori condenser C is equivalent to a step or rise on thestep voltage wave. On the negative falling edge (trailing edge) of thepulse supplied to condenser II, diode DI will conduct and dischargecondenser II, but diode D2 will not conduct, thus leaving unchanged thevoltage on condenser C acquired during the immediately precedingpositive rise of the pulse. The voltage on condenser II will becompletely discharged to ground through diode DI during this negativedrop; or putting it in other words, the negative going edge of the inputpulses is shorted to ground through diode DI. During the next positiverise in voltage caused by the succeeding pulse applied to condenser II,the condenser II will be recharged through diode D2. It will thus beseen that each time there is a positive rise in voltage applied tocondenser II, there will be an incremental increase or step-up involtage on condenser C. Although each charge on condenser C after thefirst is slightly less than the preceding one; it should be noted thatthere is no resistance whatever across condenser C, in order to avoidany leakage during the voltage step-up or charge build-up operation.

On the fifth pulse, the resulting incremental rise in voltage oncondenser C will overcome the cut-off bias on tube V2 and cause currentto conduct therein. The windings I, 2 and 3 of the pulse transformer Tare so poled that the initial flow of current in tube V2 causes theapplication of an amplified positive pulse to the grids of tubes V2 andVI. This resulting positive pulse expedites the flow of current throughtube V2 and is of suiiicient magnitude to cause tube VI to conduct. TubeV2 acts as a single-shot oscillator which amplifies the pulse fed backfrom its anode to its control grid when it starts to conduct current.

When tube VI conducts, it serves as a discharge path for the storagecondenser C. The presence of resistor R in the grid circuit of tube V2assures that the major portion of the discharge of condenser C isthrough tube VI. Since the gridcathode space path of V2 has considerablyless impedance than the anode-cathode space path of tube VI, thedischarge of condenser would in the absence of resistor R otherwise gothrough .tube V2.

Because the impedance of the anode-cathode discharge path (tube VI)varies relatively less than the impedance of the grid-cathode path oftube V2, with change in voltage of the cathode heater supply, thefrequency divider is more stable by the provision of the discharge tubeVI and the means (resistor R) for assuring the main discharge of thestorage condenser through the space path of this tube VI.

Fig. 2 is a modification of the frequency divider of Fig. 1. In thefrequency divider of Fig. 2, the pulse produced by tube V2 when itstarts to conduct, is amplified by vacuum tube V3 before being used tocause tube VI to conduct and hence discharge the storage condenser VI.It should be noted that the grid of tube V3 is connected to one end ofwinding 3 of pulse transformer T through a connection I9. Tube V3 isnormally non-conductive (like tubes V2 and VI) and obtains its cut-offbias from lead 20 which supplies a positive potential to the cathode oftube V3. The positive pulse applied to the grid of tube V3 by winding 3of transformer T, when tube V2 starts to conduct, is of sufficientmagnitude to overcome the cut-off bias on tube V3 and cause this tube toconduct. Tube V3 may act as a class C amplifier. The transformer TIserves to 4 reverse the polarity of the pulse in the output of tube V3so that it is positive when applied to the grid of tube VI.

It should be understood that the invention is independent of theparticular system shown for storing charges on condenser C, and thatother circuits may be employed to build up a predetermined charge oncondenser C in response to a desired number of input pulses, without theneces sity of using diodes DI and D2.

The following tabulation provides a comparison between the frequencydivider systems of Figs. 1 and 2 of the invention and a known systemwhich did not use the extra discharge tube VI nor the resistor R. Thedividing factor was 5:

Frequency range in kilocycles Heater Known Volts System 1 2 7. 0 760-1,200 370-1, 400 50-850 6. 5 825-1, 220 30-950 6. O 1, -1, 510 5. 5 count330-1, 300

changes The foregoing tabulation indicates that with heater volts of 7.0the frequency. range of the known system was less than 2 to 1, whilewith the system of Fig. 1 the range was 3 to 1 and with the system ofFig. 2 the range was 1'7 to 1. With heater volts of 6.5 the frequencyrange of the known system was still less than 2 to 1, while thefrequency range of the system of Fig. 2 was about 31 to 1. Nomeasurement was taken of the system of Fig. l in this particular exampleusing heater volts of 6.5.

In the embodiments of the invention successfully tried out in practice,tubes VI and V3 of Fig. 2 were part of a double triode GSNT-GT. The tubeV2 of both Figs. 1 and 2 was a 6 AC7 pentode tube connected as a triode.The pulse transformer T was a Ferranti 5029 type. The resistor R had avalue of 500 ohms.

It should be understood that the term ground used in the specificationand appended claims is not limited to an actual earth connection, but isdeemed to include any point of reference potential, such as zero radiofrequency potential.

What is claimed is:

1. A frequency divider comprising a storage condenser for storing acharge by increments in response to a series of recurring pulses, apulse transformer having a plurality of windings, an indirectly-heatedand normally non-conductive vacuum tube having a grid, a cathode and ananode, a direct current connection from said storage condenser to saidgrid through the series circuit of one winding of said pulse transformerand a resistor, said resistor being located between said grid and saidone winding, a feedback circuit for said tube including a connectionfrom said anode to another winding of said transformer, whereby saidtube forms a single-shot oscillator which passes current when the chargeon said storage condenser reaches a predetermined value, a secondindirectly heated and normally non-conductive vacuum tube having a grid,an anode and a cathode, a direct connection from the anode of saidsecond tube to the junction between said resistor and said one windingof said transformer, alternating current connections from the cathodesof said tubes to a point of reference potential, and means for applyinga pulse of positive polarity to the grid of said second tube ofsufficient magnitude to cause said second tube to conduct when saidfirst tube conducts, whereby said second tube forms a discharge path forsaid storage condenser.

2. A frequency divider comprising a storage condenser for storing acharge by increments in response to a series of recurring pulses, apulse transformer having first, second and third windings, a firstelectric tube normally biased to cutoff and having a grid, an anodeand'a cathode, a direct current connection from said storage condenserto said grid through the series circuit of said first winding and aresistor, a feedback circuit from said anode to said grid including thesecond winding of said transformer, a second electric tube normallybiased to cut-off and having a grid, a cathode and an anode, a directcurrent connection from said last anode to the junction between saidresistor and said first winding, a connection from the grid of saidsecond tube to said third winding, and capacitors coupling the cathodesof said tubes to a point of reference potential, said windings being sopoled that the fiow of current through said first tube in response to apredetermined charge on said storage condenser causes the application ofa positive pulse to the grid of said second tube of suflicient magnitude to cause said second tube to conduct.

3. A frequency divider comprising a storage condenser, means forbuilding up a predetermined charge on said condenser by increments inresponse to pulses applied to said divider and whose frequency ofoccurrence is to be divided, a first electron discharge device having acontrol grid, an anode and a cathode, a pulse transformer having first,second and third windings, a connection from said storage condenser toone terminal of said first winding, a connection including a seriesarranged resistor from the other terminal of said first winding to thecontrol grid of said device, a connection from said anode to thepositive terminal of a source of polarizing potential through the secondwinding of said transformer, a second electron discharge device havinganode, control grid and cathode electrodes, a connection from the anodeof said last device to the junction between said resistor and the firstwinding of said transformer, connections capable of passing alternatingcurrent from the cathodes of said two electron discharge devices to apoint of reference potential, means supplying bias to said devices tocause them to be normally non-conductive, and means including said thirdwinding of said pulse transformer for overcoming the cut-off bias onsaid second device when said first device passes current, said Windingsof said pulse transformer being so poled'that the flow of currentthrough said first device in response to a predetermined charge on saidstorage condenser causes the application of a positive pulse to the gridof said second device.

4. A frequency divider in accordance with claim 3, including a dampingresistor across said third winding of said pulse transformer, andcharacterized by the use of a third electron discharge device normallybiased to cut-off and arranged as an amplifier, said third device havingan input electrode coupled to said third winding and an output electrodecoupled to the grid of said second device through a phase reverser.

5. A frequency divider in accordance with claim 3, including a dampingresistor across said third winding of said pulse transformer, and adirect connection between the grid of said second device and oneterminal of said third winding.

JOHN B. ATWOOD.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,113,011 White Apr. 5, 19382,154,492 Clough Apr. 18, 1939 2,411,573 Holst et al Nov. 26, 19462,413,440 Farrington Dec. 31, 1946 2,415,918 Thomas Feb. 18, 19472,415,919 Thomas Feb. 18, 1947

